1. Field of the Invention
The present invention relates to a slot antenna incorporated in a plasma surface processing apparatus used for processing the surface of a semiconductor substrate such as a silicon wafer. More particularly, the present invention relates to a radial line slot antenna.
2. Description of the Related Art
As is well known, a typical radial line slot antenna utilized in a plasma surface processing apparatus is provided with a metal antenna guide (made of e.g. aluminum) and a disklike dielectric member (made of e.g. quartz or alumina ceramic) supported by the antenna guide. The antenna guide is formed, at its lower side, with a circular recess for accommodating the dielectric member. The slot antenna is also provided with a metal slot plate arranged under the dielectric member. The slot plate, formed with a plurality of slots, extends in parallel to the dielectric member. A microwave waveguide is connected to a central portion of the upper surface of the antenna guide. An electrical conductor extends through the inside of the waveguide to be connected to the slot plate.
In operation, microwaves led into the antenna guide are caused to propagate through the dielectric member radially outward of the dielectric member. Then, the radiated microwaves are ejected downward through the slots formed in the slot plate. Consequently, plasma is generated between the slot plate and a semiconductor substrate placed on the upper surface of a lower electrode disposed below the slot plate. The plasma thus generated is advantageously used not only for forming the various types of coatings on the semiconductor substrate but also for subjecting the semiconductor substrate to surface processing (e.g. etching).
Conventionally, the slot plate, which is rendered diametrically greater than the dielectric member, is attached, at its peripheral portions, to the antenna guide by screws. The conventional arrangement of the slot antenna has been found to have the following disadvantages.
In operation, the slot plate is heated up when plasma is generated. Since the dielectric member arranged above the slot plate has a low thermal conductivity (which is intrinsic of quartz and alumina ceramic), the heat accumulated in the slot plate is hardly absorbed by the dielectric member. Instead, the accumulated heat is conducted to the antenna guide only through the screwed peripheral portions of the slot plate. Due to this, thermal expansion of the slot plate tends to be greater at inner portions than at the peripheral portions, thereby causing the slot plate to unduly bulge downward. As a result, the clearance between the deformed slot plate and the semiconductor substrate will become uneven, whereby microwave radiation for generating plasma cannot be performed uniformly. Consequently, the plasma generation necessary for processing the semiconductor substrate will be rendered nonuniform and unstable, which is disadvantageous in performing proper surface processing for the semiconductor substrate.
To address the above problem, the slot plate may be attached, at its inner portions, to the dielectric member by screws additional to the peripheral screws connecting the slot plate to the antenna guide. In this manner, however, the heated slot plate will still be apt to bulge downward at unscrewed portions.
The present invention has been proposed under the above circumstances, and its object is to reliably reduce or even eliminate the unfavorable thermal deformation of a slot plate of a slot antenna.
According to a first aspect of the present invention, there is provided a slot antenna comprising:
a metal antenna guide formed with a recess;
a dielectric member received in the recess;
a metal slot plate held in contact with the dielectric member; and
a waveguide connected to the antenna guide for introduction of microwaves;
wherein the slot plate is uniformly supported by the dielectric member.
With such an arrangement, it is possible to prevent the slot plate from being unduly deformed downward even if the slot plate is heated.
Preferably, the slot plate may comprise a metal layer which is closely attached to the dielectric member.
Preferably, the metal layer may be formed by electroless plating. In this way, the metal layer is formed faster and at lower cost than when it is formed by applying and baking conductive paste. Further, the thickness of the resulting metal layer is advantageously uniform as a whole.
In a preferred embodiment, a protection coating may be provided for covering the metal layer.
In another preferred embodiment, at least part of the slot plate may be embedded in the dielectric member. In this manner again, downward thermal deformation of the slot plate is reliably prevented.
The slot plate may include more than one conductive layer. For instance, the slot plate may comprise a copper-plated layer and a nickel-plated layer. Of course, a conductive layer is not limited to these examples.
In a preferred embodiment, the slot plate may be provided with an annular upright portion to be held in contact with the antenna guide when the dielectric member is fitted into the recess. In this manner, the slot plate is reliably connected to the antenna guide.
Preferably, the slot antenna may further comprise a fixing piece fitted into the dielectric member. The fixing piece may be connected to the waveguide.
According to a second aspect of the present invention, there is provided a slot antenna comprising:
a metal antenna guide formed with a recess;
a dielectric member received in the recess;
a metal slot plate held in contact with the dielectric member; and
a waveguide connected to the antenna guide for introduction of microwaves;
wherein the slot plate is provided with expansion absorbing means.
With such an arrangement, thermal expansion of the slot plated is advantageously reduced or eliminated by the expansion absorbing means. Thus, even if the slot plate is not firmly fixed to the dielectric member, unfavorable thermal deformation of the slot plate is effectively prevented.
In a preferred embodiment, the slot plate may include inner and outer members defined by a series of openings formed in the slot plate and arranged in a circle.
Preferably, the inner member and the outer member may be connected by deformable linking members.
Preferably, the series of openings of the slot plate may be closed by the antenna guide. Alternatively, these openings may be closed by suitable metal pieces which may be mounted on the dielectric member or slot plate itself or other members.
In a preferred embodiment, the slot plate may be positionally fixed at a central portion thereof as well as at peripheral portions thereof.
Preferably, the slot antenna may further comprise urging means for pressing a peripheral portion of the slot plate against the antenna guide. The urging means may be springs such as coned disc springs.
The slot antenna may further comprise a second dielectric member arranged under the slot plate for supporting the slot plate. In place of the second dielectric member, use may be made of a metal supporting member arranged under the slot plate for supporting the slot plate. In this instance, the metal supporting member may be formed with a plurality of openings for exposing the slot plate.
Preferably, the dielectric member may be made of AlN ceramic material.
In a preferred embodiment, the antenna guide may be formed with a groove extending around the recess for circulating coolant. The groove may be closed by the slot plate.
The slot antenna may further comprise an additional dielectric member arranged in facing relation to the slot plate so that a hermetical passage for circulating nonconductive coolant is formed between the additional dielectric member and the slot plate.
Preferably, the additional dielectric member may be arranged parallel to the slot plate.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.